GMC 1990 Light Truck Repair Manual page 327

• If the backlash is incorrect, adjust the sleeves
as necessary. Always maintain the " one
notch" preload on the side bearings. EXAM­
PLE. If it is necessary to turn the RIGHT
sleeve IN one notch, the LEFT sleeve must be
turned OUT one notch.
• To increase backlash, turn the left sleeve in,
and turn the right sleeve out an identical
amount. To decrease backlash, turn the right
sleeve in and turn the left sleeve out an identi­
cal amount.
10. When the backlash is correct, mark the position of
the sleeves so they can be kept in the same loca­
tion.
GEAR TOOTH CONTACT
PATTERN CHECK
Before final assembly of the differential, a gear tooth
contact pattern check must be performed.
It should be noted that a gear tooth contact pattern
check is NOT a substitute for adjusting pinion depth
and backlash as previously outlined. It is a method to
L-VAN FRONT AXLE 4C5-11
verify the correct running position of the ring gear and
the drive pinion. Gear sets which are not positioned
properly may be noisy, or have a short life, or both.
The best contact between the ring gear and the drive
pinion for low noise level and long life can be assured
with a pattern check.
GEAR TOOTH NOMENCLATURE
The side of the ring gear tooth which curves out­
ward, or is convex, is referred to as the " drive" side.
The concave side is the " coast" side. The end of the
tooth nearest the center of ring gear is referred to as
the " toe" end. The end of the tooth farthest away
from the center is the " heel" end. The toe end of the
tooth is smaller than the heel end, (figure 28).
TEST
1. Wipe oil out of carrier and carefully clean each
tooth of the ring gear.
2. Use gear marking compound and apply this mix­
ture sparingly to all ring gear teeth using a medi­
um stiff brush. When properly used, the area of
pinion tooth contact will be visible when hand load
is applied.
3. Apply a load until a torque of 54-70 N-m (40-50 ft.
lbs.) is required to turn the pinion.
A test made without loading the gears will not
give a satisfactory pattern. Turn the companion
flange with a wrench so that the ring gear rotates
one full revolution then reverse the rotation so that
the ring gear rotates one revolution in the opposite
direction. Excessive turning of the ring gear is not
recommended.
4. Observe the pattern on the ring gear teeth and
compare with figure 29.
ADJUSTMENTS AFFECTING TOOTH CONTACT
Two adjustments can be made which will affect the
tooth contact pattern. These are backlash and the posi­
tion of the drive pinion (pinion depth) in the carrier. The
effects of bearing preloads are not easily seen on hand
loaded teeth pattern tests. These adjustments should
be within specifications before proceeding with the
backlash and the drive pinion adjustments.
It may be necessary to adjust both pinion depth and
the backlash to obtain the correct pattern.
The position of the drive pinion is adjusted by
increasing or decreasing the shim thickness between
the pinion head and the inner race of the rear bearing.
The shim is used in the differential to compensate for
manufacturing tolerances. Increasing the shim thick­
ness will move the pinion closer to the center line of
the ring gear.
Backlash is adjusted by means of the side bearing
adjusting sleeves which move the entire case and ring
gear assembly closer to, or farther from the drive pin­
ion. (The adjusting sleeves are also used to set side
bearing preload). To increase backlash, turn the left
sleeve in and turn the right sleeve out an identical
amount. To decrease backlash, turn the right sleeve in
and turn the left sleeve out an identical amount.
It is important that the contact pattern be centrally
located up and down on the face of the ring gear teeth.